Alternative Polyolefin Composite Veil/Compatibilizing Mat Materials

ABSTRACT

A compatibilized polyolefin/polyolefin composite material includes a polyolefin/polyolefin composite substrate and a reinforcing mat formed from reinforcing fibers and a thermoplastic polymer powder. The mat may also incorporate an optional emulsion polymer binder. In addition the compatibilized polyolefin/polyolefin composite material may incorporate an additional film layer so that the mat is sandwiched between the substrate and the film layer. A method of producing such materials from a to polyolefin/polyolefin composite substrate that is topologically/mechanically bonded to a reinforcing mat formed from reinforcing fibers and thermoplastic polymer powder is also described.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention relates generally to improving surface smoothness,surface hardness, and compatibilizing polyolefin or polyolefin compositematerials to functional polymers. A method of producing such materialsfrom a polyolefin/polyolefin composite substrate that istopologically/mechanically bonded to a reinforcing mat formed fromreinforcing fibers and thermoplastic polymer powder is described.

BACKGROUND OF THE INVENTION

Plastic sheet materials made from polyolefin or polyolefin compositematerials are widely used in the manufacture of molded articles. Suchmaterials suffer from bonding issues, little to no surface abrasionresistance, coupled with composite form process issues. Accordingly,when used for certain applications such as, for example, high impactpaneling, woven fiberglass/polyolefin materials have a tendency todevelop sink marks that many consumers find detrimental to theiraesthetic appearance. It should also be appreciated that polyolefin andpolyolefin composite materials are often difficult to adhere or bond toother materials. This can limit the application of these materialsparticularly where decorative attributes are required.

A need is therefore identified for a way to effectively provide surfaceenhancements and improved bondability to polyolefin and polyolefincomposite materials. Preferably, the fiber reinforcement will beaccomplished in a manner that not only provides increased strength andrigidity when employed with straight polyolefin materials but alsocompatibilizes the polyolefin and polyolefin composite materials forbetter bonding to other materials and also functions to provide smoothersurfacing and a wider range of decorative possibilities. The presentinvention successfully achieves these goals while also minimizing theapplication of heat to the polyolefin/polyolefin composite materialprior to molding into the final product shape. Thus, a number ofimportant properties including surface energy, surface smoothness, andimprovements in impact, flexural and tensile strengths of straightpolyolefin materials can be achieved.

SUMMARY OF THE INVENTION

In accordance with the purposes of the present invention as describedherein, a compatibilized polyolefin/polyolefin composite material isprovided. That material comprises a polyolefin/polyolefin compositesubstrate and a reinforcing mat. Bonding between chemically incompatiblegroups within the mat and polyolefin is achieved through a mechanicalbonding or topological affect whereby the polyolefin material flows intothe reinforcing mat layer, gets caught between the more viscous matbinder, and achieves a mechanical interlock.

The reinforcing mat is formed from reinforcing fibers selected from agroup consisting of glass fibers, carbon fibers, aramid fibers, kenaffibers, hemp fibers, cellulose fibers and mixtures thereof and athermoplastic polymer powder selected from a group of materialsconsisting of phenolic powders, phenoxy powders, polyester melt adhesivepowders, modified polyethylene powders, PVC/PVDC copolymer powders, EVApowders, PVA powders, acrylic powders, polyester powders, PVC/PVAccopolymer powders and mixtures thereof.

The phenolic powders include novalak, cresol type and resorcinol typepowders. More specifically describing the invention, the phenoxy basedepoxy powders include various melting point materials made possible byincreasing the degree of polymerization between Bisphenol A andepichlorohydrin. Polyester melt adhesive powders include low molecularacids, such as terephthalate, adipic, isophthalic, phthalic, azelaic,diacids, (linoleic, oleic and soybean) and sebacic, reacted with diolssuch as ethylene glycol, 1,4 butanediol, 1,6-hexanediol and1,4-cyclohexanedimethanol. In all cases, the melting point of the matbinder should either exceed the melting point of the polyolefin or theselected binder must be considerably more viscous than the selectedpolyolefin.

The modified polyethylene based resin powders include acid modifiedand/or maleic anhydride grafted polyolefins combined with a filler toincrease the specific gravity of the powder to at least 1 gi/cm³. Thepolyester powders include thermosetting type polyesters that employmultifunctional acids and diols. The acrylic powders include higherglass transition acrylics like polymers formed from methacrylic acid,acrylic acid and methyl methacrylate or thermosetting acrylic materialsthat employ functional hydroxy groups like 2-hydroxyethyl methacrylate,2-hydroxypropyl methacrylate and the like.

The reinforcing fibers provided in the mat have a diameter of betweenabout 10 to about 23 microns and a length of between about 0.25 to 1.5inch. The reinforcing fibers are provided in the reinforcing mat atbetween about 20 to 40 weight percent and the thermoplastic polymerpowder is provided at between about 60 to 80 weight percent. Inaccordance with an additional aspect of the present invention the matmay also incorporate an emulsion polymer binder. That emulsion polymerbinder may be an acrylic emulsion. Where the mat incorporates anemulsion polymer binder, the reinforcing fibers are provided at betweenabout 20 to 40 weight percent, the thermoplastic polymer powder isprovided at between about 40 to 75 weight percent and the polymer binderis provided at between about 5 to 10 weight percent. The purpose of theemulsion binder is to minimize possible fiber dusting complaints duringthe final consolidation step by providing further bonding ease of thethermoplastic powder to the reinforcing glass fibers.

In accordance with still another aspect of the present invention, thecompatibilized polyolefin/polyolefin composite material may furtherinclude a film against the mat so that the mat is disposed between thefilm and the polyolefin/polyolefin composite substrate. The film isformed from a material selected from a group consisting of PVC, PVC/PVAccopolymer, PVC/PVDC copolymer, PVDC, ABS, acrylic, polyester andmixtures thereof.

In accordance with an additional aspect of the present invention, amethod of compatibilizing a polyolefin/polyolefin composite material isprovided. The method includes contacting a reinforcing mat formed fromreinforcing fibers selected from a group consisting of glass fibers,carbon fibers, aramid fibers, kenaf fibers, hemp fibers, cellulosefibers and mixtures thereof and a thermoplastic polymer selected from agroup of materials consisting of phenolic powders, phenoxy based epoxypowders, polyester melt adhesive powders, modified polyethylene basedresin powders, PVC/PVDC copolymer powders, EVA powders, PVA powders,acrylic powders, polyester powders, PVC/PVAc copolymer powders andmixtures thereof with a polyolefin/polyolefin composite substrate. Stillfurther, the method may include a polymer binder in the mat such as anacrylic emulsion. Additionally, the method includes a step of applyingsufficient temperature and pressure for a sufficient time to consolidatethe mat and substrate.

More specifically describing the invention, the method includesselecting a pressure of between about 50 to about 300 psi forapplication to the mat and substrate at a temperature between about 350to about 450EF for a period of time of between about 10 to about 300seconds.

In addition, the method may include the step of adding a film againstthe mat. The film is selected from a group of materials consisting ofPVC, PVC/PVAc copolymer, PVC/PVDC copolymer, PVDC, ABS, acrylic,polyester and mixtures thereof. Films are normally applied for variouspurposes including decorative, UV resistance, or enhanced bondability todecals.

Advantageously, the resulting compatibilized polyolefin/polyolefincomposite material is only subjected to one heat treatment to both (a)consolidate the mat and substrate together and (b) mold the materialinto its final shape. Since this is done in a single heating step, thematerial is subjected to fewer heat cycles and the material accordinglyhas observed less thermal cycles. It is also provided with veilpossibilities and the polyolefin/polyolefin composite material is mademore compatible for binding with other materials. When employing wovenglass/polyolefin composites, sink marks often occur without the presenceof a surfacing veil. This invention provides surfacing veilcharacteristics coupled with enhanced surface bondability in a singlestep. Although alternative methods of bonding polyolefin materials toother materials exist, as is made possible by grafting acrylic acid,maleic anhydride, and other function groups, and/or by the incorporationof corona discharge, plasma treatment, or flame treatment, thesealternative methods can not provide smoothening effects, a harder morescratch resistant surface, or permanent chemical changes withoutgrafting reactions.

In the following description there is shown and described the preferredembodiment of this invention simply by way of illustration of severalmodes best suited to carry out the invention. As it will be realized,the invention is capable of other different embodiments and its severaldetails are capable of modification in various, obvious aspects allwithout departing from the invention. Accordingly, the drawings anddescriptions will be regarded as illustrative in nature and not asrestrictive.

BRIEF DESCRIPTION OF THE DRAWING

The accompanying drawing incorporated in and forming a part of thespecification, illustrates several aspects of the present invention andtogether with the description serves to explain the principles of theinvention. In the drawing:

FIG. 1 is a schematical cross sectional view showing a first embodimentof the compatibilized polyolefin/polyolefin composite material of thepresent invention; and

FIG. 2 is a schematic cross sectional view showing a second embodimentof the compatibilized polyolefin/polyolefin composite material of thepresent invention.

Reference will now be made in detail to the present preferred embodimentof the invention, an example of which is illustrated in the accompanyingdrawing.

DETAILED DESCRIPTION OF THE INVENTION

Reference is now made to FIG. 1 schematically illustrating one possibleembodiment of the compatibilized polyolefin/polyolefin compositematerial of the present invention. The material 10 includes apolyolefin/polyolefin composite substrate 12 and a reinforcing mat 14.

The polyolefin/polyolefin composite substrate may, for example, be madefrom high density polyethylene, polypropylene, polybutylene, mixed withvarious chemical additives such as heat stabilizers, UV stabilizers,metal deactivators, and the like possibly combined with grafted speciesthat incorporate acrylic acid or maleic anhydride to promote thebondability of the polyolefin to whatever glass fiber form is employed.Composite forms may include injection moldable grades,extrusion-compression molded long fiber grades, GMT forms as for examplean Azdel® type product, or in a woven roving form as for example aTwintex® product grade.

The reinforcing mat 14 is formed from reinforcing fibers and athermoplastic polymer powder. The reinforcing fibers are selected from agroup consisting of glass fibers, carbon fibers, aramid fibers, kenaffibers, hemp fibers, cellulose fibers and mixtures thereof. Whenmoisture resistance is required, the thermoplastic polymer powder isselected from a group of hydrolysis resistant materials includingphenolic powders, phenoxy powders, polyester melt adhesive powders,modified polyethylene powders and PVC/PVDC copolymer powders. Whenmoisture resistance is not a requirement for a particular application,the thermoplastic polymer powder may also be selected from other,nonhydrolysis resistant melt adhesive powders, polyvinyl acetatepowders, EVA powders, PVC/PVAc copolymer powders and any mixturesthereof.

Still more specifically describing the invention, the phenolic powdersmay include novalak, cresol type and/or resorcinol type powders. Thephenoxy based epoxy powders may include various melting point materialsmade possible by increasing the degree of polymerization betweenBisphenol A and epichlorohydrin. The polyester melt adhesive powdersinclude lower molecular acids, such as terephthalate, adipic,isophthalic, phthalic, azelaic, diacids (linoleic, oleic and soybean)and sebacic, reacted with diols such as ethylene glycol, 1,4 butanediol,1,6-hexanediol and 1,4-cyclohexanedimethanol. The modified polyethylenebased resin powders include acid modified and/or malaic anhydridegrafted polyolefins combined with a filler to increase the specificgravity of the powder to at least 1 gm/cm³. Acrylic powders includehigher glass transition acrylics like polymers formed from methacrylicacid, acrylic is acid and methyl methacrylate or thermosetting acrylicmaterials that employ functional hydroxy groups like 2-hydroxyethylmethacrylate, 2-hydroxypropyl methacrylate and the like. If crosslinkingis employed with the acrylic version, it must be light to allow theacrylic to seal the composite from polyolefin bleed through.

The mat 14 may also, optionally, incorporate an emulsion polymer binder.That polymer binder may take the form of an acrylic emulsion.

The reinforcing fibers present in the mat typically have a diameterbetween about 10 to about 23 and more typically, about 10 to about 16micron and a length between about 0.25 to about 1.5 inch. Still further,the reinforcing fibers are provided at between about 20 to about 40weight percent while the thermoplastic polymer powder is provided atbetween about 60 to about 80 weight percent of the mat.

The embodiment of the present invention shown in FIG. 2 includes asubstrate 16, a mat 18 and a film 20. Thus, the mat 18 has the substrate16 on one side and the film 20 on the other. The substrate 16 of thesecond embodiment is identical to the substrate 12 described in detailabove when discussing the first embodiment shown in FIG. 1. Similarly,the mat 18 is identical to the mat 14 described in detail above whendiscussing the first embodiment. The film 20 is formed from a materialselected from a group consisting of PVC, PVC/PVAc copolymer, PVC/PVDCcopolymer, PVDC, ABS, acrylic, polyester and mixtures thereof.

Like the mat 14 of the first embodiment, the mat 18 of the secondembodiment may also incorporate an emulsion polymer binder such as anacrylic emulsion. Additionally, the reinforcing fibers of the mat 18also have a diameter of between about 10 to about 23 micron and a lengthof between about 0.25 to about 1.5 inch. The mat 18 has reinforcingfibers present in an amount of between about 20-40 weight percent,thermoplastic polymer powder present in an amount of between about 40and about 75 weight percent and polymer binder present in an amount ofabout 5 to about 10 weight percent. The compatibilizedpolyolefin/polyolefin composite material 22 of the second embodiment hasan overall density of between about 0.9 to about 1.9 gm/cm³, dependingupon the level of glass reinforcement, with the substrate 16 present atbetween about 87 to about 99 weight percent, the mat 18 present atbetween about 0.7 to about 10 weight percent and the film 20 present atbetween about 0.3 to about 3 weight percent.

The material 10 illustrated in FIG. 1 is made by a method that may bebroadly defined as including the steps of: (1) contacting a reinforcingmat formed from reinforcing fiber selected from a group consisting ofglass fibers, carbon fibers, aramid fibers, kenaf fibers, hemp fibers,cellulose fibers and mixtures thereof and a thermoplastic polymerselected from a group of materials consisting of phenolic powders,phenoxy based epoxy powders, polyester melt adhesive powders, modifiedpolyethylene based resin powders, PVC/PVDC copolymer powders, EVApowders, PVA powders, acrylic powders, polyester powders, PVC/PVAccopolymer powders and mixtures thereof with a polyolefin/polyolefincomposite substrate and (2) applying sufficient temperature and pressurefor a sufficient time to consolidate the mat and thepolyolefin/polyolefin composite substrate. The material 22 illustratedin FIG. 2 is also made by means of these contacting and applying stepsbut includes the additional step of adding a film 20 against the mat 18so that the mat 18 is disposed between the film 20 and the substrate 16prior to the applying step. If a single sided film application is to beperformed, the film thickness should be minimized to prevent warpingissues. If this is not possible, then a symmetric structure would benecessary where a film layer, mat layer, polyolefin/polyolefincomposite, mat layer, and film layer arrangement would be necessary toprevent warpage.

In either of the materials 10, 22 shown respectively in FIGS. 1 and 2,the mat 18 is produced by forming an aqueous suspension of discontinuousfibers and an aqueous suspension of the thermoplastic polymer powder orpowders. This is typically accomplished with agitation in a mixing tank.The resulting combined aqueous suspension, slush or pulping medium isthen processed into a wet-laid, sheet-like material by machines such ascylinder Fourdinier machines or other technologically advanced machinerysuch as the Stevens Former, Roto Former, Inver Former and VertiFormermachines. Specifically, the combined aqueous suspension is depositedfrom a head box onto a moving wire screen or on to the surface of amoving wire-covered cylinder. The combined aqueous suspension or slurryon the screen or cylinder is then processed into a nonwoven, sheet-likemat by the removal of water. This is typically accomplished by a suctionor vacuum device. This process is exemplified in, for example, U.S. Pat.No. 5,393,379 and is well known in the art.

After the mat is formed into a dewatered sheet it may be densified bypressing with a flat press or sending through calendering rolls. Thedensification of the mat after drying is particularly useful to increasethe tensile and tear strength of the mat. Drying may be completed eitherby air drying at ambient temperature or oven drying.

The prepared mat is then positioned to contact and rest upon anunderlying polyolefin/polyolefin composite substrate. The optional film20 may then be added on top of the mat when the presence of the film isdesired in the final product. Once the substrate 12, 16, mat 14, 18 andoptional film 20 (if present) are positioned in contact with each other,the material 10, 22 is molded into a desired shaped by closing theappropriate mold platens for forming the desired article and applying apressure to the material 10, 22 of between about 50 to about 300 psiwith the platens at a temperature of between about 350 to about 450EFfor a period of time of between about 10 to about 300 seconds. This heatand pressure serves to activate the thermoplastic polymer powder in themat 14, 18 and to force the polymer of the substrate 12, 16 and film 20(if present) to partially flow into the mat layer where itmechanically/topologically interlocks with the mat binder in the mannerof jigsaw puzzle pieces or a Velcro fastener (note interlocking shownat, for example, I in the drawing figures). Polyolefin bleed through themat layer is prevented by employing sufficient basis weight mat, such as0.2-0.08 lb/ft² basis weights and by selecting thermoplastic binderresins which seal the mat layer from surging polyolefin flow in the zdirection. The material 10, 22 is then cooled by cooling the platens orby some other means to set the polymer materials and thereby consolidatethe substrate 12, 16 with the mat 14, 18 and the film 20 (if present).

The compatibilized polyolefin/polyolefin composite materials 10, 22 ofthe present invention exhibit a number of unique properties. Due toexposure to a limited number of heating cycles, impact, flexural andtensile strengths may be improved. The addition of the mat also providesveil possibilities for the polyolefin composites and serves tocompatibilize the polyolefin/polyolefin composite substrate for bondingto other materials. The mat also provides an effective hard surfacelayer for the polyolefin/polyolefin composite based substrate. Wherehydrolysis resistant powders are utilized in the mat moisture resistancemay be enhanced if the polyolefin composite interface was insufficientto prevent wicking.

The following examples are presented to further illustrate theinvention, but it is not to be considered as limited thereto.

EXAMPLE 1

A 22 oz/yard², seventy weight percent, woven Twintex® material, 0.06lb/ft² mat material comprising of 70 weight percent glass fibers coupledwith 30 percent by weight rigid PVC may be combined to form a bondablesurface by placing both materials flat into a preheated mold at 370° F.,holding both materials together for approximately 30 seconds at 100 psi,and cooling the assembly to 240° F. prior to removing the assembly fromthe press. The resulting composite will form a strong mechanical bondthat is unbreakable even under extreme temperature and moisture cyclingsuch as consecutively submitting the material to boiling water and a dryice environments.

EXAMPLE 2

A 44 oz/yard², seventy weight percent, woven Twintex® material, 0.06lb/ft² mat comprising of 70 weight percent glass fibers coupled with 30percent by weight PVC, and a white rigid PVC film of 0.003 milthickness, may be combined to form a hard decorative surface by placingboth materials flat into a preheated mold at 370° F., holding bothmaterials together for approximately 30 seconds at 100 psi, and coolingthe assembly to 240° F. prior to removing the assembly from the press.The resulting composite will form a strong mechanical bond that isunbreakable even under extreme temperature and moisture cycling such asconsecutively submitting the material to boiling water and a dry iceenvironments.

EXAMPLE 3

A 44 oz/yard², seventy weight percent, woven Twintex® material, 0.06lb/ft² mat comprising of 65 weight percent glass fibers coupled with 30percent by weight PVC, and 5 weight percent acrylic binder, and a whiterigid PVC film of 0.003 mil thickness, may be combined to form a harddecorative surface by placing both materials flat into a preheated moldat 370° F., holding both materials together for approximately 30 secondsat 100 psi, and cooling the assembly to 240° F. prior to removing theassembly from the press. The resulting composite will form a strongmechanical bond that is unbreakable even under extreme temperature andmoisture cycling such as consecutively submitting the material toboiling water and a dry ice environments.

The foregoing description of the preferred embodiment of the inventionhas been presented for purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed. Obvious modifications or variations are possible inlight of the above teachings.

The embodiment was chosen and described to provide the best illustrationof the principles of the invention and its practical application tothereby enable one of ordinary skill in the art to utilize the inventionin various embodiments and with various modifications as are suited tothe particular use contemplated. All such modifications and variationsare within the scope of the invention as determined by the appendedclaims when interpreted in accordance with the breadth to which they arefairly, legally and equitably entitled.

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 15. (canceled)16. A method of compatibilizing a polyolefin/polyolefin compositematerial, comprising: contacting a reinforcing mat formed fromreinforcing fibers selected from a group consisting of glass fibers,carbon fibers, aramid fibers, kenaf fibers, hemp fibers, cellulosefibers, and mixtures thereof and a thermoplastic polymer selected from agroup of materials consisting of phenolic powders, phenoxy based epoxypowders, polyester melt adhesive powders, modified polyethylene basedresin powders, PVC/PVDC copolymer powders, EVA powders, PVA powders,acrylic powders, polyester powders, PVC/PVAc copolymer powders andmixtures thereof with a polyolefin/polyolefin composite substrate;applying sufficient temperature and pressure for a sufficient time toconsolidate said mat and said polyolefin/polyolefin composite substrate.17. The method of claim 16 wherein prior to said contacting step themethod includes preparing an aqueous suspension of said reinforcingfibers and said thermoplastic polymer, forming a sheet-like materialfrom said aqueous suspension, dewatering said sheet-like material anddensifying said sheet-like material to produce said reinforcing mat. 18.The method of claim 16, further including selecting for application tosaid mat and said substrate a pressure of between about 50 to about 300psi and a temperature of between about 350 to about 450° F. for a periodof time between about 10 to about 300 seconds.
 19. The method of claim16, further including adding a film against said mat.
 20. The method ofclaim 19, further including selecting said film from a group ofmaterials consisting of VC, PVC/PVAc copolymer; PVC/PVCD copolymer,PVDC, ABS, acrylic, polyester and mixtures thereof.
 21. The method ofclaim 19, further including selecting for application to said film, saidmat and said substrate a pressure between about 50 to about 300 psi anda temperature between about 350 to about 450° F. for a period of timebetween about 10 to about 300 seconds.
 22. The method of claim 19,further including providing a polymer binder in said mat.
 23. The methodof claim 19, further including providing an acrylic emulsion in saidmat.